Method for continuous production of a basic cupric sulfate



March 13, 1962 MOTOZO HlRAO ETAL 3,025,136

METHOD FOR CONTINUOUS PRODUCTION OF A BASIC CUPRIC SULFATE Filed June 20. 1958 4 Sheets-Sheet 1 M NT B Om A MW WMU K I MKY E I WM,

March 13, 1962 MOTOZO RAO ETA 3,025,136

METHOD FOR c T oUs PRODUCT N OF A BA CUPRIC SULFATE Filed June 20. 1958 4 Sheets-Sheet 2 M. HIRAO K. HARUTA Y. KUWATSUKA E. MUNEKATA S. IMAMOTO INVENTORS March 13, 1962 MOTOZO HIRAO ETAL 3,025,136

METHOD FOR CONTINUOUS PRODUCTION OF A BASIC CUPRIC SULFATE Filed June 20. 1958 4 SheetsSheet 3 M. HIRAO K. HARUTA Y- KUWATSUKA E. MUNEKATA S. IMAMOTO INVENTORS \N fL/ March 13, 1962 Filed June 20. 1958 FIG. 6

4 Sheets-Sheet 4 M. HIRAO K. HARUTA Y. KUWATSUKA g E. MUNEKATA & IMAMOTO INVENTOR-S 3,025,135 METHOD FOR CUNTINUOUS PRUDUCTIGN UF A BASlC CUPRIC SULFATE Motozo Hirao, Kazuo Haruta, and Yasuhiko Kuwatsulra, Noheoka, and Eiji Munelrata and Sadasuke lmarnoto, Tokyo, Japan, assignors to Asahi Kasei Kogyo Kahushiki Kaisha, Osaka, Llapan, a corporation of .lapan Filed June 20, 1958, Ser. No. 743,430 Claims. (Cl. 23-125) This invention relates to a continuous method for the manufacture of basic cupric salt of high cupric hydroxide content suitable for the production of a cuprammonium rayon and to an apparatus thereof.

Generally speaking, the basic cupric salt which has heretofore been known for use in the production of a cuprammonium rayon, i.e., a cupric salt obtained, for example, by a reaction at about 90 C. of a cupric sulfate solution with a sodium carbonate solution or aqueous ammonia has a large particle size and it is readily subjected to treatments such as filtration, sedimentation, washing and the like. On the other hand, a great deal of heat is required for the hot reaction thereof and yet the product obtained has a mol ratio of (Eu/S0 as low as 3.5 or so. Thus, when it is used to produce a spinning solution, a great amount of caustic soda is necessary in the process of dissolving cellulose to activate or convert into cupric hydroxide an inactive copper which has been combined with a sulfate radical. Accordingly the spinning solution obtained contains a great amount of sodium sulfate, which has been found to be detrimental to the quality of the product yarns (US. Pat. No. 2,758,013; Japanese Pat. Nos. 134,172. and 149,821, etc). Accordingly, various technical researches have been developed and practical methods have been proposed to overcome the abovementioned difiiculties by the use of basic cupric sulfate having as high cupric hydroxide content or mol ratio of Cu/SO, as possible for the production of the spinning solution, such as referred to in the above US. Pat. No. 2,758,013 and Japanese Pat. Nos. 113,262, 181,338, 198,735 and the like. However, these methods have also encountered many difficulties because they are too complicated to be practiced on a commercial scale; the nature of the resulting precipitates is not always suitable for such treatments as filtration, sedimentation, washing and the like; it is very difficult to obtain a constant composition; and the like. By way of detailed explanation as to this point, reference is made to the process of the abovementioned Japanese Patent No. 198,735. This is the only process in which a chemically pure cupric hydroxide can be obtained under commercial conditions. As shown in the chemical Equations 1 and 2 described below, this process may first produce the basic cupric sulfate of comparatively good sedimentability having a mol ratio of 3 or so, which is, then, separated from the mother liquor and subjected to the action of aqueous ammonia to produce the cupric hydroxide. This twostep process is so complicated and the various factors such as sedimentability, filterability, etc. involved therein are not satisfactory to a commercial production.

The method of US. Patent No. 2,758,013 or Japanese Patent No. 181,338 wherein a cupric sulfate solution and ammonia are caused to react with stirring at room temperature under the controlled conditions of pH is easier in operation and has been commercially eliected. By the use of this method, the basic cupric sulfate having a mol 25,136 Patented Mar. 13, 1962 ratio of (Du/S0 of 7 or so may be obtained, but the particle size of the sediment is so small and the distribution is so wide (05-5 1, average 2.5 1. or so) that it is quite inferior to the commonly used basic copper by the hot process as described before in various points such as sedimentabi'lity and filtrability, etc. Moreover, a great amount of ammonium sulfate is adsorbed in the sediment to the extent that it is difiicult to wash and remove, which result in a poor actual mol ratio of 4.5 or so including the adsorbed ammonium sulfate with much fluctuation. Consequently, it is not too much to say that when such basic cupric salt is used in the manufacture of the spinning solution for cuprammoniumrayon the results which could be expected from the used of the described basic cupric salt having a high mol ratio can not be substantially obtained.

It is an object of this invention to provide a method for continuously and commercially manufacturing a basic cupric salt at ordinary temperatures which has a high mol ratio i.e. about 7, with little fluctuation, has few impurities, and is easily subjected to treatments, continuously washing said basic cupric sulfate with water, subjecting it to the reaction with aqueous ammonia and continuously supplying it as a cuprammonium solution for use in the production of the spinning solution for cuprammonium rayon, wherein the difficulties encountered in the conventional methods can be overcome. It is another object of this invention to provide an apparatus thereof.

In order that the invention may be fully understood it will now be described with reference to the accompanying drawings, in which- FIG. 1 is a longitudinal sectional view along line BB of FIG. 2 of the apparatus of the present invention.

FIG. 2 is a cross sectional view of the apparatus of FIG. 1.

FIG. 3 is a longitudinal sectional view of the washing device for the products obtained by the use of the apparatus of FIG. 1.

FIG. 4 is a cross sectional view of the device of FIG. 3.

FIG. 5 is the washing device of which a part of wall is cut oflf.

FIG. 6 is a schematic view of the apparatus for carrying the present process.

According to the present invention, a cupric solution, such as cupric sulfate, and an alkaline solution, such as aqueous ammonia or cupric tetrammine sulfate solution are continuously supplied into a reaction apparatus which has a reaction chamber provided with a stirrer and a concentration-separation chamber for the reacting product or sediment assembled in one apparatus, and the reaction takes place under predetermined constant temperatures and pH. A part of the sediment which has been sedimented and concentrated in the concentrationseparation chamber by gravity is made a seeding liquor, which is caused to circulate without destroying the particleswithin the range of the predetermined cycle numbers and at a certain constant value. Thus, the reaction can take place under the conditions of high copper concentration.

The starting materials, i.e. a cupric salt solution and an alkaline solution, are continuously and simultaneously supplied. A cupric sulfate solution may be used as the cupric salt solution. The concentration thereof may be l-5 g./ cc., suitably 2.5 g./ 100 cc. calculated as Cu. Another reactant to be used is aqueous ammonia or a solution of cupric tetrammine sulfate. It is preferable that the concentration is 210 g./ 100 cc. of NH when the former is used, and 1-5 'g./ 100 cc. as Cu when the latter is used. It is most convenient for the starting materials to use solutions recovered in recovery process as cupric sulfate solution and cupric tetrammine sulfate solution. Additional cupric sulfate solutions equivalent to the amount lost in the recovery process must be added. Concentrations of the starting materials depend upon this copper recovery process. In practice, the above mentioned concentrations are moderate. On supplying the two reactants simultaneously and at a constant ratio, the following reaction takes place.

use. For example, rate of sedimentation of particle relative to temperature is as follows:

M./h. 15 C 1.8 10 C 1.3 5 C- 0.5

On the other hand, if the temperature is more than 30 C., a precipitate having mol ratio of as low as 4 is apt to form, and the produced precipitate has so poor stability that it is readily converted to a basic salt having lower mol ratio.

M01 ratio of M01 ratio of Temp., C. (Du/S in pre- (Jo/S0 after cipitate on 12 hrs.

formation The rate of stirring is not critical.

Some of the sediment resulted from the above reaction is caused to circulate as a seeding liquor. The other sediment is withdrawn and passed to the washing device as shown in FIGS. 3, 4 and 5 described in detail below. In the above circulation, care must be taken as to the cycle number so that the seeding liquor should not be destroyed. The reason why some of a sediment should be circulated is that it is essential in the present invention to effect the reaction at the high concentration of copper.

The cycle number is a numerical value calculated according to the following equation, the suitable value being between and 50 depending upon the particle size of the sediment.

x: The copper concentration newly introduced into the reaction chamber, i.e. copper freshly fed to the reaction chamber (g.) per 100 cc. of liquid volume freshly fed to the same chamber.

: The copper concentration of the circulating liquid (forward), that is, copper concentration in a circulating liquid which is withdrawn from the reaction chamber and fed to a concentration-separation chamber (g./100 cc.).

z: The copper concentration of the circulating liquid (backward), that is, copper concentration in a circulating liquid which is concentrated in a concentrationseparation chamber and returned to the reaction chamber (g./l00 cc.).

If cycle number A is less than the figure above referred Cycle number A:

to, sufiicient growth of the precipitated particles is inhibited and particle size becomes small, whereby a precipitate having the desired settling and being easily filterable and washable, cannot be produced. While if cycle number A is more than the figure above referred to, the particles are destroyed in a recycling course, growth of particles is inhibited, and moreover, smooth separation of settling particle phase from supernatant liquid phase is prohibited, for contacting surface of both phases is turbulated.

By selecting the above conditions, the sedimented copper salt crystal nuclei can grow very compactly with uniform particle size and excellent sedimentability, which becomes easy of access to the treatments such as filtration and washing. Moreover, this has a high mol ratio (about 7) of less fluctuation and contains lms impurities, such as A1, Fe, SiO etc., therein.

Since the supernatant liquid involved in the production of basic cupric salt or the supernatant liquid which has flown out from the eifluent device of the concentrationseparation chamber of FIG. 1 hereinafter explained contains 1000-1500 m g/l. of copper, this can be separated and recovered as basic cupric sulfate by neutralizing it with sulfuric acid or waste copper-containing acid resulting from the spinning process. The reaction in this case may be indicated in the following chemical equation, the basic cupric sulfate having a mol ratio of Cu/SO of about 4 being produced.

The mol ratio of the basic cupric sulfate recovered from the supernatant liquid is 4 as described before, but has few impurities so that the sulfate can be used for the production of the spinning solution by mixing therewith the above basic cupric sulfate of high mol ratio. In this case, the amount of the recovered copper is less than ,5 of that of the basic cupric sulfate of high mol ratio, so that the substantial reduction of the actual mol ratio does not occur by the use of the mixture. When the countercurrent continuous water-washing device as explained below is used, it is convenient to conduct this mixing in a hopper in admixture with the slurry of the basic cupric sulfate of high mol ratio because washing with water may concurrently be effected.

It is of course possible in the neutralization of the above supernatant liquid to use the above apparatus for continuously manufacturing the basic cupric salt. In such a case, similar advantages may also result wherein the sediment which is readily washable and has uniform particle size, excellent sedimentability, few impurities and a mol ratio of less fluctuation can be obtained.

The waste supernatant liquid which has been stripped of copper may be passed to an ion-exchange vessel wherein the remaining copper in amount of -300 mg./l. can be adsorbed and removed. Thereafter, the ammonium sulfate contained therein can be recovered either as such by concentration as described in US. Patent No. 2,758,- 013 or as aqueous ammonia by distillation after addition of alkali such as lime and the like.

Similarly the waste washing water resulting from the counter-current continuous water-Washing device may be stripped of the copper contained therein in an ion-exchange vessel and can be used as a source of ammonium sulfate or ammonia as described just above if the ammonium sulfate content thereof is suitably high, e.g., more than 1%.

The general process will readily be understood from FIG. 6.

This invention can be carried out in the apparatus as shown in FIG. 1 and FIG. 2. This apparatus is similar in construction to an accelerator, and a settler which has been known as water clarification apparatus but is functionally different therefrom in that the agitation in the reaction chamber can be controlled depending upon the particular conditions of reaction and the optimum stirring conditions can be set so as to obtain the predetermined sediment of basic cupric salt and that the sedimentation and concentration in the sedimentation-separation chamber can be conducted as satisfactorily as possible depending upon the sedimentability of the sediment. In the case of water clarification, the sediment flock tends to be destroyed by a slight power so that it can not stand vigorous agitation, whereas in the sedimentation of basic cupric salt, the sediment is strong enough to stand such vigorous agitation because it is necessary to circulate the sedimentas a concentrated seeding liquor (for example, -25 g./100 cc. as Cu) at the cycle number of 10 to 50; the particle size is so large that the sedimentation rate is greater and the local accumulation tends to occur, which necessitates a vigorous agitation in the reaction chamber (for example, 200 rpm. in the apparatus having a capacity of 25 kg./hr. of Cu); and the sediment is quite dense. Also in the case of water clarification, the product is a supernatant liquid, while in the apparatus for the manufacture of basic cupric salt, the product must be the sediment itself. Accordingly, the sedimentation-concentration should be in conjunction with the subsequent water-washing device, such that the capacity of concentration is very high. Thus, the apparatus of the present invention has such a special design as described before in the structure of the reaction chamber and the concentration-separation chamber, which distinguishes itself from the conventional water-clarification apparatus.

The reaction chamber A and the concentration-separation chamber B are concentrically established in one apparatus, both of which are separated from each other by an outer tube 2 and an inner tube 1 of a draft tube, and a compartment wall 3 having a shape similar to an inverted funnel. The reaction chamber A is provided with a stirrer 4, to which feed pipes 8 and 9 are open for respectively introducing the reactant liquids, a cupric salt solution and an alkaline solution. The pipes may preferably be closely located against the stirrer 4 so that, on introduction of the reactants, they are intimately mixed with each other to produce a homogeneous solution. The ends of the pipes form cycles on which a plurality of holes are perforated. The concentration-separation chamber B is made of an outer wall 6 or the cylindrical section and a bottom wall 7 or the cone section and the outer tube 2 of the draft tube. When both reactant liquids are continuously and simultaneously fed from the feed pipes 8 and 9 to the chamber A and caused to react with a vigorous agitation by the stirrer 4, a sediment of basic cupric salt is produced, which is then carried upwards by the action of the stirrer 4 and passed through the inner and outer tubes 1 and 2 into the chamber 13 where the sedimentation-concentration takes place. Some of the sediment is withdrawn by a suitable slurry pump such as a diaphragm pump through a sediment-withdrawing pipe 10 while the supernatant liquid is caused to flow out from an efiluent device 11 and is continuously withdrawn from a supernatant liquid exit pipe 12. A lower end of pipe 10 opens near the bottom of the chamber A so that it takes up concentrated precipitate which is concentrated in chamber B and circulated in chamber A, without clogging. A major part of the sediment is caused to circulate into the chamber A as a concentrated seeding liquor through a passageway which is established in the bottom part of the chamber B. The stirrer 4 in the reaction chamber is provided with a movable wing means 5 which can be set at any angle and favors circulation of liquid in a definite direction from downwards to upwards. Also the inner tube 1 of the draft tube is provided with an adjustment window 13 which opens to any degree by the up and down movement of an adjustment rod 14. By setting the wing means 5 of the stirrer 4 at a suitable angle and adjusting the degree of opening the window 13 of the inner tube 1, it is possible to adjust the cycle number A of the sediment to suitable values of 10 to 50.

The concentration-separation chamber B is so constructed that the cone-shaped bottom wall 7 inclines at an angle more than 40 and the ratio of heights or L /L of the cylindrical section and the conical section is less than 1 so as to respond to the sedimentability of the basic cupric salt having large particle size. Because of such special design, it is possible that the sediment of the basic cupric salt which has large particle size and is very easy to sediment does not accumulate on the bottom part of the reaction chamber or other parts, resulting in a smooth circulation and highly eflicient concentration. In FIG. 1 and FIG. 2, 16 is a stirring shaft for rotating the stirrer 4 and the adjustable wing means 5 fastened thereto. Wing means 5 draw liquid from the central space 17 in the interior of funnel-shaped wall 3, which central space 17 forms the upper portion of chamber A- upwardly through and past the hollow stirrer 4 into the space about stirrer shaft 16, inside inner tube wall 1; 19 is a partioning plate for making the flow in the draft tube uniform; and 20 are baiile plates. Units shown in FIGS. 1 and 2 must be made of a material which is not corroded by either reactants or products; for instance, they can be made of stainless steel.

In the operation of the above described apparatus, the reactant liquids or an alkali and a cupric salt solution, for example, aqueous ammonia such as 5 g./ cc. NH;.; and a cupric sulfate solution such as Cu 2.5 g./ 100 cc. solution, or a solution of cupric tetrammine sulfate such as Cu 2.5 g./1 00 cc. solution and a cupric sulfate solution such as Cu. 2.5 g./100 cc. solution, are continuously fed through the pipes 8 and 9 into the reaction chamber A at the predetermined rate shown in the chemical Equations 3 and 4. In the chamber A, the reaction is efiected with the action of the stirrer 4 while adjusting the pH in the chamber at a constant value (6.5-7.5).

The resulting product is guided by the tubes 1 and 2 into the chamber B wherein the sedimentation and concentration take place by virtue of gravity. A major part of the resulting sedimentation liquid is caused to circulate from the bottom of the chamber B through 15 into the chamber A. Thus, the reaction chamber may be maintained under such high copper concentration as 10-25 g./ 100 cc. (as Cu). As the interface between the supernatant liquid and the sediment in the chamber B is not disturbed by the circulating liquid coming from the chamber A due to the action of the tubes 1 and 2, it is possible not only to completely separate the supernatant liquid from the upper part of the chamber B and cause it to overflow therefrom, but also to continuously withdraw the sediment from the bottom of the chamber, part of which is under quite concentrated conditions such as a slurry density of 20-50 g./ 100 cc. or a Cu concentration of 10-25 g./100 cc. In the withdrawal of the sedimentation liquid, it is effected in such a manner that the amount thereof will be balanced with that of the fresh cupric salt introduced into the chamber A. Also the temperatures of the reactant liquids should be adjusted prior to the introduction into the reaction chamber so that the temperature of the chamber may be kept at constant (l0 -30 C.).

When the above apparatus for the manufacture of basic cupric salt is used and the reaction takes place under the above conditions, the circulating liquid becomes a concentrated seeding liquor of Cu 10-25 g./ 100 cc. so that the particles of the sediment grow densely in a uniform and large size (15-40 average 25 and the sedimentation rate of slurry reaches 1-3 m./hr. at the above copper concentration which is comparable with that of the hot process basic cupric salt. Subsequent treatments such as washing and sedimentation will be very easy. Thus, when a continuous water-washing device -as shown in FIGS. 3, 4 and 5 as a slurry water-washing device is used, a small amount of water (2-5 times as much to the amount of slurry) is suflicient to wash it easily and continuously, whereby the basic cupric salt having excellent qualities and high purity with high mol ratio, i.e. about 7, can be obtained. For example, it is possible to continuously obtain a basic cupric salt in a concentrated form which has a mol ratio of 7 or so (about 6.5 even when the adsorbed ammonium sulfate is included) in a less fluctuation and contains very little impurities such as SiO Ca, Mg, Al, Fe, organic substance and others which are detrimental to the dissolving or the spinning processes. This serves, after continuous addition thereto of concentrated aqueous ammonia (for example, 25 g./ 100 cc.) in a ratio of NH /Cu=2-2.5 for example, as Schweizers reagent which may be continuously fed to the production of a spinning solution.

The water-washing device shown in FIGS. 3, 4 and 5 is made of anti-corrosive material such as stainless steel or has lead-lining. It is provided with a simple rotary type distribution pipes 25 which serve concurrently as an upper agitation wing for the cylindrical tank 34 and from which the sedimented copper salt slurry is allowed to be ejected into the tank 34. The water for washing is sprayed out from the distribution pipes 27 having collecting wings and fixed in the bottom part in a co-axial relation with the pipes 25. By bringing the sedimented copper salt into counter-current contact with the water, the distribution of the sedimented copper in the tank 34 is made uniform so that a very high washing efficiency and uniform washing effect may be realized with a minimum amount of water.

In the water-washing device, the sedimented copper slurry withdrawn from units of FIGS. 1 and 2 and pumped out by slurry pump is continuously introduced from an upper feed tube 21 into a hopper 22, from which it flows down through a double pipe 24 concentrically fixed with a rotary agitation shaft 23 into 2 to 5 radial slurry distribution pipes 25 which have a plurality of small openings 41 directed downwards. The slurry is discharged from these openings into the tank 34. The washing water is passed through the lower tube 26 into the pipes 27 and sprayed into the tank 34 through a plurality of Openings in the above pipes which are directed downwards. The pipes 27 are also provided with wings 33 for collecting the sediment. If desired, other agitation wings 28 may be attached to the shaft 23. The shaft 23 can be driven by a motor 29. The sediment in the slurry which has been discharged from the openings 41 of the pipes 25 flows down under the effect of gravity through the tank 34, coming into counter-current contact with the water passing upwards from the bottom for uniform washing, reaching the inclined bottom 42 and being introduced into the sediment storage space 30 by means of the collecting wings 33 in which storage space 30 it is sedimented and concentrated to a predetermined slurry density and discharged out through a tube 31 by means of a slurry pump such as a diaphragm pump. The liquid in the slurry is passed upwards under dilution by the washing water into the uppermost overflowing zone 32, from which it flows out and is removed through an exit tube 43.

In FIGS. 3, 4 and 5, 35 is a transmitting means from the motor 29 to the rotary shaft 23; 36 is an agitation wing for the sediment storage 30, 38 is a cover for the agitation shaft; 39 is a support for the washing-water distribution pipes 27; 40 is a support for the wings 36; and 44 is an upper bearing for the agitation shaft 23.

The continuous washing device as shown in FIGS. 3, 4 and 5, hereinafter called counter-current continuous water-washing device, may be used either alone or in combination of two sets. The advantage of the use of the connected two sets is that, by decreasing the amount of washing water in the first set so that the concentration of ammonium sulfate contained in the waste washing liquor may be made higher, the ammonium sulfate or ammonia can be recovered from the waste.

An example of the present invention is indicated as follows:

In the apparatus similar to that shown in FIG. 1 and FIG. 2, 5 g./100 cc. of aqueous ammonia and 2.5 g./ 100 cc. (as Cu) of cupric sulfate solution are caused to react with each other in a continuous manner while the pH and the temperature in the reaction chamber are respectively adjusted to 6.87.0 and 28 C., and the cycle number A is maintained at 15. As a result, the sediment withdrawn at a value of Cu 20 g./ 100 cc. is continuously obtained, which has the composition as indicated (a) in the following table. In the table, the composition (b) is that subsequently washed by two steps of the counter-current continuous water-washing device as shown in FIGS. 3, 4 and 5. As compared with the analysis (0) of the basic cupric salt which has been commercially obtained by the conventional method (Japanese Patent No. 181,338), it is obvious that this has a very high purity as well as a high mol ratio.

Table In the above table, the bottom parentheses show the mol ratios exclusive of adsorbed ammonium sulfate.

In this example, the analysis of the supernatant efiluent is as follows.

Cu 1350 mg./l. (NH SO 3.51 g./100 cc.

This copper salt may be subjected to the reaction with the waste copper-containing liquid (Cu 0.98 g./ 100 cc.; H 4.95 g./ cc.) in the above described apparatus. The reaction conditions are adjusted to pH 6.3, temperature 28 C. and cycle number (A) 20. The withdrawn sediment has a copper concentration of 25 g./ 100 cc. (as Cu). This sediment may be mixed in the hopper of the counter-current continuous water-washing device with the above-described sediment of the basic cupric sulfate of high mol ratio and washed so that both may be well mixed.

The supernatant effluent of the basic cupric sulfate of high mol ratio, which has been stripped of its copper as far as the same was present in the form of basic cupric sulfate by the above mentioned means, may still contain residual copper. When it is removed in the ion-exchange vessel 4.10 g./ 100 cc. of aqueous ammonium sulfate may be obtained in this case, which can be mixed with the washing water of the counter-current continuous waterwashing device and concentrated for use in the recovery of ammonium sulfate or added with lime and distilled to produce aqueous ammonia.

In this case the copper content in the sediment coming from the counter-current continuous water-washing device is 12.07 g./ 100 cc., which can be continuously supplied, after addition of 24 g./ 100 cc. of aqueous ammonia, as a solution of tetrammine copper hydroxide having the following composition for the production of spinning solution for cuprammonium rayon.

In FIG. 6, ammonia and copper salt solutions are respectively fed from their storage tanks 45 and 46 to basic copper salt continuous manufacturing apparatus 50 by pumps 47 and 48. The copper salt solution passes heat-exchanger 49 by the way, where the solution is heated or cooled so as to correspond to reaction temperature in 50. Sedimented copper slurry in 50 is continuously withdrawn by diaphragm pump 51 and fed to the first washing apparatus 53 where the slurry is washed With water, and then to the second washing apparatus 55 through diaphragm pump 54. The washed slurry in 55 is withdrawn by pump 56 and fed to copper-concentration controller 57 where the slurry is diluted to a definite copper concentration, for example, 12 g./100 cc. of Cu. The slurry is fed to a tetrammine copper hydroxide manufacturing apparatus 52 where an ammonia aqueous solution containing 24 g./100 cc. NH is added so that NH /Cu is a definite value (for example, 2.25) and a tetrammine copper hydroxide solution containing for example,

Cu 6.50 g./100 cc. NH 15% is formed. The solution is fed by pump 60 to a storage tank 62 via a heat-exchanger 61 and, if desired, is subjected to dissolution step of a cellulosic material via pump 63.

A supernatant liquid from 50 is fed by pump 52 to a supernatant neutralization unit 64 where it is neutralized with sulfuric acid. Sedimented basic copper salt thus formed having mol ratio of 4 is fed by diaphragm pump 65 to first washing device 53 where the copper salt, together with sediment having higher mol ratio from 50, is washed with water. Supernatant from 64 is passed through ion-exchangers 66 and 67 to split off residual copper and then fed to ammonia recovering unit (not shown).

We claim:

1. A continuous method of producing a basic cupric sulfate suitable for use in the manufacture of cuprammonium rayon, comprising,

(a) mixing with stirring at a temperature of about 10 to 30 C. and a pH of about 6.5 to 7.5, an aqueous cupric sulfate solution and a member selected from the group consisting of aqueous ammonia solution and aqueous alkaline cupric ammine salt solution in such amounts that the molar ratio of CuzNH is about 7:12 and the molar ratio of Cu:SO in the final product is about 7:1, thus producing a precipitate of basic cupric sulfate,

(b) continuously withdrawing part of the resulting slurry, and permitting the withdrawn part to settle to obtain a concentrate containing from about 10 to 25 grams Cu per 100 cubic centimeters of the resulting slurry in a settling zone,

() recirculating the slurry from said settling zone into fresh mixture obtained by (a) at a substantially constant recycling rate A of about 10 to 50, A being equal to wherein x is the concentration of Cu in the cupric sulfate solution freshly introduced into (a), y is the concentration of Cu in the slurry being withdrawn under (b), and z is the concentration of Cu in the slurry being recirculated under (0), thereby obtaining a basic cupric sulfate substantially corresponding to the formula 6Cu(OH) .CuSO and consisting of granules of about 15 to 40 microns. 2. A continuous method of producing a basic cupric sulfate suitable for use in the manufacture of cuprammonium rayon, which comprises:

(a) mixing in aqueous solution at a temperature of from 10 to 30 C. and a pH within the range of from 6.5 to 7.5 cupric sulfate having a concentration corresponding to from about 1 to 5 grams of Cu er 100 cc. of solution with a member selected from the group consisting of ammonia in a concentration of from about 2 to grams of NH per 100 cc. of solution and complex cupric ammine sulfate in a concentration corresponding to from about 1 to 5 grams of Cu per 100 cc. of solution, thus producing a precipitate of basic cupric sulfate,

(b) continuously withdrawing part of the resulting slurry, and permitting the withdrawn part to settle to obtain a concentrate containing from about 10 to 25 grams Cu per cubic centimeters of the resulting slurry in a settling zone,

(0) recirculating the slurry from said settling zone into fresh mixture obtained by (a) at a substantially constant recycling rate A of about 10 to 50,.A being equal to wherein x is the concentration of Cu in the cupric sulfate solution freshly introduced into (a), y is the concentration of Cu in the slurry being withdrawn under (b), and z is the concentration of Cu in the slurry being recirculated under (c), thereby obtaining a basic cupric sulfate substantially corresponding to the formula 6Cu(OH) .CuSO and consisting of granules of about 15 to 40 microns. 3. A continuous method of producing a basic cupric sulfate suitable for use in the manufacture of cuprammonium rayon which comprises:

(a) mixing in aqueous solution at a temperature of from 10 to 30 C. and a pH within the range of from 6.5 to 7.5 cupric sulfate in a concentration corresponding to from about 1 to 5 grams of Cu per 100 cc. of solution with ammonia in a concentration of from about 2 to 10 grams of NH per 100 cc. of solution,

(b) continuously withdrawing part of the resulting slurry, and permitting the withdrawn part to settle to obtain a concentrate containing from about 10 to 25 grams Cu per 100 cubic centimeters of the resulting slurry in a settling zone,

(c) recirculating the slurry from said settling zone into fresh mixture obtained by (a) at a substantially constant recycling rate A of about 10 to 50, A being equal to wherein x is the concentration of Cu in the cupric sulfate solution freshly introduced into (a), y is the concentration of Cu in the slurry being Withdrawn under (b), and z is the concentration of Cu in the slurry being recirculated under (0), thereby obtaining a basic cupric sulfate substantially corresponding to the formula 6Cu(OH) .CuSO and consisting of granules of about 15 to 40 microns. 4. A continuous method of producing a basic cupric sulfate suitable for use in the manufacture of cuprammonium rayon which comprises:

(a) mixing in aqueous solution at a temperature of from 10 to 30 C. and a pH within the range of from 6.5 to 7.5 cupric sulfate in a concentration corresponding to from about 1 to 5 grams of Cu per 100 cc. of solution with tetrammine cupric sulfate in a concentration corresponding to from about 1 to 5 grams of Cu per 100 cc. of solution,

(b) continuously withdrawing part of the resulting slurry, and permitting the withdrawn part to settle to obtain a concentrate containing from about 10 to 25 grams Cu per 100 cubic centimeters of the resulting slurry in a settling zone,

(c) recirculating the slurry from said settling zone into fresh mixture obtained by (a) at a substantially constant recycling rate A of about 10 to 50, A being equal to wherein x is the concentration of Cu in the cupric sulfate solution freshly introduced into (a), y is References Cited in the file of this patent UNITED STATES PATENTS Gulbrandsen July 9, Rowe Jan. 2, Bishop et al. Oct. 13, Kalinske May 18, Hadsel June 12, Munekata Aug. 7, 

1. A CONTINOUS METHOD OF PRODUCING A BASIC CUPRIC SULFATE SUITABLE FOR USE IN THE MANUFACTURE OF CUPRAMMONIUM RAYON, COMPRISING. (A) MIXING WITH STIRRING AT A TEMPERATURE OF ABOUT 10* TO 30*C. AND A PH OF ABOUT 6.5 TO 7.5, AN AQUEOUS CUPRIC SULFATE SOLUTION AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF AQUEOUS AMMONIA SOLUTION AND AQUEOUS ALKALINE CUPRIC AMINE SALT SOLUTION IN SUCH AMOUNTS THAT THE MOLAR RATIO OF CU: NH3 IS ABOUT 7:12 AND THE MOLAR RATIO OF CU:SO4 IN THE FINAL PRODUCT IS ABOUT 7:1, THUS PRODUCING A PRECIPITATE OF BASIC CUPRIC SULFATE, (B) CONTINOUSLY WITHDRAWING PART OF THE RESULTING SLURRY, AND PERMITTING THE WITHDRAWN PART TO SETTLE TO OBTAIN A CONCENTRATE CONTAINING FROM ABOUT 10 TO 25 GRAMS CU PER 100 CUBIC CENTIMETERS OF THE RESULTING SLURRY IN A SETTLING ZONE, (C) RECIRCULATING THE SLURRY FROM SAID SETTLING ZONE INTO FRESH MIXTURE OBTAINED BY (A) AT A SUBSTANTIALLY CONSTANT RECYCLING RATE A OF ABOUT 10 TO 50, A BEING EQUAL TO 